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"Flight 3411 from Chicago to Louisville was overbooked. After our team looked for volunteers, one customer refused to leave the aircraft voluntarily and law enforcement was asked to come to the gate. We apologize for the overbook situation." United Airlines said in a statement.

The incident ignited social media outrage, with "United" a trending term on Twitter, Facebook and Google.

United Airlines chief executive Oscar Munoz addressed the latest controversy in a statement posted overnight on the airline's website.

"This is an upsetting event to all of us," Mr Munoz said, adding that the airline was conducting a "detailed review of what happened."

"We are also reaching out to this passenger to talk directly to him and further address and resolve this situation," he said.

Tyler Bridges, who posted video of Sunday's incident on Twitter, wrote: "not a good way to treat a Doctor trying to get to work because they overbooked."

He described passenger reaction on the plane as "disturbed."

"Kids were crying," he said.

Mr Bridges also wrote that the man appeared bloodied by his encounter with law enforcement and posted video showing him later running back on the plane, repeatedly saying, "I have to go home."

The man appeared to be pacing and disoriented.

Airlines are allowed to involuntarily bump passengers off overbooked flights, with compensation, if enough volunteers cannot be found, according to the US Department of Transportation.